JPS6042161B2 - Production method of uranium mononitride - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing uranium mononitride using uranium dioxide as a raw material.

More specifically, the present invention relates to a method of converting uranium dioxide into uranium carbide and reacting this uranium carbide with ammonia or a hydrogen/nitrogen mixture to produce uranium mononitride. Uranium oxide is desirable as a raw material for producing uranium mononitride, a nuclear fuel material, because of its low production cost.

In particular, uranium dioxide is commonly used because the reaction can be easily controlled. In a manufacturing method using uranium dioxide as a raw material, uranium dioxide is reduced with carbon and nitrided. Therefore, the main impurities in uranium mononitride produced from uranium dioxide are oxygen and carbon. Many efforts have been made to date to reduce the amount of these impurities. A conventional method for producing uranium mononitride from uranium dioxide will be described below.
The first method involves mixing uranium dioxide and carbon in a molar ratio of exactly 1:2, and heating the mixture at 1,500 to 17 μC in a nitrogen stream to produce uranium mononitride.

The advantage of this method is that the production reaction is completed in a single reaction step. However, (1) high temperatures are required for the reaction to proceed quickly, (2) it is difficult to mix uranium dioxide and carbon at an accurate molar ratio of 1:2, and (3) there is a high Even if uranium nitride is manufactured with the skill and technology of uranium nitride, it has drawbacks such as relatively high concentrations of impurities such as 0.1% by weight of oxygen and 0.15% by weight of carbon. Therefore, in order to reduce the amount of impurity oxygen, a second method was devised in which the amount of carbon in the reducing agent is slightly excessive and this excess carbon is removed by hydrogen. This method uses uranium dioxide and carbon in a molar ratio of 1:2.
．． 14-2.16 and this mixture was heated under nitrogen at 1600 °C.
This is a production method in which excess carbon is removed with hydrogen after reaction at ~170°C.

In this method, uranium monochloride is produced through the fifth step of reducing nitriding, removing free carbon, liberating solid solution carbon, removing free carbon again, and decomposing higher nitrides. This method includes (1) easy mixing of uranium dioxide and carbon;
(2) It has the advantage of being able to reduce the oxygen impurity in uranium mononitride by as much as 0.1% by weight, but it has the disadvantage of requiring a complicated manufacturing process that involves five steps. 5. An object of the present invention is to provide a new method for producing uranium mononitride with a low concentration of impurity oxygen, which eliminates the drawbacks and drawbacks of conventional production methods.

The present invention aims to produce uranium mononitride through two steps: converting uranium dioxide into an oxygen-free compound and converting this into uranium mononitride. Specifically, uranium dioxide and carbon are mixed at a molar ratio of 1:3 to 4. This mixture was heated to 1350°C.
Uranium carbide (UC uranium monocarbide,
U2C3 diuranium tricarbide, UC2 uranium dicarbide) are produced. This step is called a carbonization reaction step. Uranium carbide is further added to an ammonia stream or a hydrogen/nitrogen mixture stream.
Uranium mononitride is produced by heating at 400-1750° C. until the hydrocarbons are exhausted. This is called a nitriding reaction step. After the nitriding reaction process is completed, the ammonia or hydrogen/nitrogen mixed gas is replaced with helium, or the reactor is evacuated and cooled. Thus, uranium mononitride is obtained. Next, the present invention will be explained with reference to examples.

Note that in this specification, the mixing ratio of gases is % by volume.

Example 1 Uranium dioxide and carbon (graphite) were mixed in molar ratios of 1:3 and 1:4.

Each mixture was molded into pellets with a diameter of 7, a height of 2-3wn, and a weight of 0.5fI. This pellet is placed in an induction heating furnace.
After heating at 1600℃ in a helium stream for 2 hours and exhausting carbon monoxide, the heating furnace is heated with an ammonia stream at a flow rate of 0.5e/min or 8% hydrogen + 92% nitrogen or 75% hydrogen at a flow rate of 1.0e/min. +25% nitrogen flow and 1400～
It was heated at 1750° C. until the discharge of hydrocarbons had ended. After the reaction was completed, the inside of the reactor was evacuated to replace it with helium and cooled. As a result of the above, the lattice constant is 4.8892 to 4.889
Six uranium mononitrides were produced. Table 1 shows the analytical values for impurities in uranium mononitride produced under various conditions. Approximately 9 to 1 F during the nitriding reaction process! Oxygen in uranium mononitride subjected to heating reaction between Tf is 0.023 to 0.05%, and carbon is 0.
．． It was between 0.009 and 0.044% by weight.

As shown in Table 1, the amount of impurities in uranium mononitride produced by the method of the present invention is conventionally the first method (oxygen 0.0% by weight, carbon 0.15% by weight) and the second method (oxygen 0.1% by weight). 1% by weight, carbon 0.2% by weight). In Example 1, the carbonization reaction step was heated at 1600°C, but it is well known that this reaction step proceeds at 1350°C or higher.

The nitriding reaction step was heated at 1400 to 1750°C. 14
If it is below 00°C, the speed of the decarburization reaction in the nitriding reaction step is slow, and if it is above 1750°C, it is not practical because the life of the heating furnace will be shortened.

The hydrogen/nitrogen mixed gas used was 8 to 75% hydrogen. Since the decarburization reaction rate in the nitriding reaction step decreases at a hydrogen concentration of 8% or less, and there is a risk of explosion at a hydrogen concentration of 75% or more, neither was used.

As is clear from the above, the method of the present invention is as follows: (1) The method of the present invention converts uranium dioxide into uranium carbide containing no oxygen (carbonization reaction step), and converts this into nitride (nitridation reaction step). It consists of two steps.

(2) Uranium dioxide and carbon may be mixed at a molar ratio of 1:3 to 4.

(3) There is no residual unreduced uranium dioxide.

(4) The purity of uranium mononitride is high and comparable to that made from uranium metal. It has the following characteristics.

Claims (1)

[Claims] 1. Mix 3 to 4 moles of carbon to 1 mole of uranium dioxide, and add this mixture to 135% in vacuum or in an inert atmosphere.
After heating at 0°C or higher to complete exhaustion of carbon monoxide, further heat with a stream of ammonia or 8 to 75% hydrogen by volume.
After heating at 1,400 to 1,750°C in a 25% by volume nitrogen gas mixture to complete exhaustion of hydrocarbons, replace the ammonia or hydrogen/nitrogen mixture with an inert gas or evacuate and cool. A unique method for producing uranium mononitride.